1. Field of the Invention
The subject invention generally relates to dock levelers, and more specifically to a dock leveler whose deck is raised by an inflatable member.
2. Description of Related Art
Loading docks often include a dock leveler to facilitate the loading or unloading of a truck's cargo. The dock leveler provides a bridge that material handling equipment and personnel can use to travel between a loading dock platform and the bed of the truck. Dock levelers usually include a deck or ramp that can pivot about its rear edge to raise or lower its front edge. Often a lip plate extends from the front edge of the deck and is adapted to engage the rear of the truck bed. The lip plate is usually movable between a stored, retracted position and an extended, vehicle-engaging position. The pivotal movement of the deck enables the dock leveler to set the lip plate on or remove it from the truck bed.
To pivot a deck, a dock leveler usually includes some type of actuator that extends, expands or otherwise moves to force the deck upward. Downward movement of the deck may be achieved by relying on weight of deck or by physically pushing the deck back down by way of an external force or weight, such as the weight of a person standing on the deck.
There are currently a variety of well-known actuators available. Some common ones include, hydraulic cylinders, pneumatic cylinders, coil springs, high-pressure air springs, linear motors, and inflatable actuators. Each has their advantages and features that may be preferred by the end user for various reasons, such as cost, reliability, durability, appearance, safety, and strength or power to lift a particular deck. The various actuators may also have their limitations.
For example, some inflatable bag actuators provide limited deck-lifting force due the strength or shape of the actuator's inflatable bag. A bag's lifting force is, in part, a function of the air pressure within the bag and the contact area between the bag and the underside of the deck. A bag's strength may be limited by not only the strength of the bag's material, but also the strength of the seams that hold the bag together. A bag may experience the highest stress adjacent the maximum cross-sectional area of the bag's internal volume. In cases where the maximum cross-sectional area is significantly greater than the contact area between the bag and the deck, the maximum stress on the bag may be unnecessarily high at the bag's maximum cross-sectional area. The bag's strength may be further weakened if the bag's seams are adjacent that cross-sectional area. Examples of such bag designs appear to be disclosed (i.e., the disclosure is of limited detail) in the following U.S. Pat. Nos. 6,216,303; 5,651,155; 5,500,968; 5,481,774; 5,471,693 and 5,446,938.
Since the underside of dock leveler's deck often includes spaced apart support beams, a generally rigid load-supporting plate may need to be attached to the beams to provide a broad, flat surface against which the bag may push. Such a support plate, as disclosed in U.S. Pat. Nos. 5,522,108 and 5,802,651, not only adds cost to the dock leveler, but also adds to the weight of the deck and thus adds to the weight the bag must lift. A similar plate is also disclosed in U.S. Pat. Nos. 6,267,447 and 6,267,448.